1. Livebearing Without Parental Care (Viviparity):
- In viviparous livebearers, the female carries fertilized eggs internally and provides nourishment to the embryos through a placenta-like structure. Examples include guppies, platies, and swordtails.
2. Ovoviviparity (Egg Retention):
- Ovoviviparous species retain the fertilized eggs within the female's body until they hatch internally, but they do not provide direct nourishment to the embryos. When hatched, the young are fully formed and free-swimming. Examples include mollies and some killifish species.
3. True Livebearing (Placental Viviparity):
- True livebearers, such as Goodeidae family members like the Mexican molly (Goodea atripinnis), have a specialized structure called a trophont that develops within the female's ovary. This structure provides nutrients and oxygen to the developing embryos.
4. Mouthbrooding:
- Mouthbrooding livebearers, such as cichlids and some livebearer families like the Aplocheilidae (killifish), carry fertilized eggs or live fry in their mouths until they hatch or reach a certain stage of development. Both male and female parents may perform mouthbrooding behavior.
5. Womb Pouch or Marsupium:
- Some livebearer species, like seahorses (Syngnathidae) and some pipefish, have unique structures for carrying developing young. In seahorses, males possess a brood pouch or marsupium where females deposit their eggs for fertilization and development.
6. Pouch-Forming Structures:
- Certain livebearer species have abdominal pouches or skin folds that enclose and protect developing young until they are ready to be released. For instance, the sailfin molly (Poecilia latipinna) has a specialized caudal pouch where the fry are nurtured.
7. Free-Swimming Fry:
- A few livebearer species, such as the platyfish (Xiphophorus maculatus) and some Goodeidae members like the splitfin livebearer (Xenotoca eiseni), release live young that are already free-swimming and capable of independent feeding from birth.
It's important to note that different species within the same family or genus can exhibit variations in their reproductive strategies, and not all livebearer species fall into one specific category.